1. Field of the Invention
The present invention relates to a communication device, a communication method, a program and a communication system.
2. Description of the Related Art
In recent years, a global positioning system (GPS) is known as positioning technology that uses satellite signals transmitted from satellites. With positioning technology using GPS, it is possible for a terminal that receives satellite signals from satellites to perform positioning to determine its own position.
Here, for example, even when the number of satellites is approximately thirty in total, when the terminal performs positioning using the satellite signals, it generally receives signals from three or four of the approximately thirty satellites. For that reason, the terminal requires time to identify from which satellites to receive the satellite signals with which to perform positioning. As a result, when the terminal performs positioning, if the terminal ascertains in advance orbit information (almanac data, for example) that indicates an orbit of a satellite and position information that indicates a general position of the terminal itself and so on, it is possible to reduce the amount of time required to identify which satellite to receive satellite signals from for use in performing positioning.
Furthermore, when the terminal performs positioning, if the terminal ascertains in advance accurate satellite orbit information (ephemeris data, for example), it is not necessary to download accurate satellite orbit information from the satellite for use in performing positioning. Therefore, if the terminal ascertains in advance accurate satellite orbit information, it is possible to reduce the time required to perform positioning. For example, Japanese Patent Application Publication No. JP-A-2001-74826 discloses technology in which a device that is capable of determining its own position by receiving satellite signals is placed at a base station, and accurate satellite orbit information that is included in satellite signals received by the base station is acquired by the terminal and used to perform positioning of the terminal.